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Community and Q&A

Form Following Function in a Hot Humid Climate

Hugh Stearns | Posted in General Questions on

Over the last thirty years the materials and techniques that makeup Building Science have changed a great deal. What has not changed is residential design. That is especially true in the south where most developments require a large percentage of thermal mass on the outside of a home. Given what we know about materials and techniques how should design adapt in a hot humid climate? For example, now that we have rid ourselves of vented attics, should we go ahead and bring that space all the way into conditioned space with vaulted ceilings?  And what of those steeply pitched roofs? Shouldn’t we reduce that pitch and extend the eaves? If we aren’t going to use masonry, what are wise materials to consider for exterior veneer and what do those lines need to create a balanced design? It seems wise to bring thermal mass inside the home to moderate heat loads. Is this at all cost-effective and what does this look like? What do these things tell us about design? This is a very general question. I’m looking for help in stepping out of the very stale box of convention from a slow to change industry.  I’m not so much asking about materials and techniques, though I’m happy to hear about that, I’m asking how these things should impact design.

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Hugh,

    That's true. Despite what the enthusiasts who frequent GBA hope, houses are shaped much more by culture and marketing than building science. You see that clearly when houses in the suburbs of Phoenix look very similar to those in Edmonton or Seattle. What divides them pales compared to what they share, and most of the adaptation to a specific place occurs by unseen modifications to the buildings envelopes, not changes in their form.

    What would houses look like if they were shaped more strongly by the demands of their disparate climates?

    I have some idea how it might play out where I live in the PNW, with large overhangs, covered outdoor space, and strategies to introduce lots of light. https://www.osburnclarke.com/joes

    Houses in hot arid regions might benefit by the roof being detached from the structure below like this one: https://www.jetsongreen.com/2009/06/desert-modern-rimrock-ranch-house.html

    Unfortunately I don't know enough about humid, hot climates to have any idea what might work. Maybe looking at structures facing similar challenges elsewhere in the world would yield some good ideas.

    1. Hugh Stearns | | #3

      Malcolm,

      Thanks. Those are nice examples of homes that are both mindful of and well connected to their environments. Connection to nature is an important part of our design approach.

  2. Expert Member
    Zephyr7 | | #2

    I would suggest looking into the architecture in the Carribbean Islands. They have heat, they have humidity, and they have houses that work for their conditions. What I've typically seen are a lot of open spaces to allow breezes to blow THROUGH the home, and a lot of tile, which I imagine also helps make the house feel cooler.

    Bill

    1. John Clark | | #6

      They also get rebuilt quite frequently.

  3. Hugh Stearns | | #4

    Bill,

    We pay close attention to vernacular architecture and draw from it. The introduction of air conditioning changes the equation quite a bit. I have had the good fortune of having had a few designers from South America. It is amazing how much design changes when you go from wood framing to structural brick. One of these designers laughed and said, "Americans build their homes from sticks, did they learn nothing from the three little pigs."

  4. GBA Editor
    Martin Holladay | | #5

    Hugh,
    You might want to read "Hot-Climate Design."

    1. Hugh Stearns | | #9

      Thanks, Martin!

  5. John Clark | | #7

    CZ1-2, CZ 3 Marine
    For the US I'm going to say wind and flood resiliency will continue to be primary design considerations because the cost to insure is only going to continue to rise.

    1. Hugh Stearns | | #10

      John,

      I would say this is a significant issue, even without pressure from the insurance industry. We see huge amounts of damage from houses too low to the ground. In our area, almost all are too low.

      1. Expert Member
        Malcolm Taylor | | #12

        John,

        Our codes and bylaws here on Vancouver Island mandate the height of buildings above bodies of water to address flood risk from storm surge, high rivers, and tsunamis. It's nuts if other jurisdictions don't.

        1. John Clark | | #14

          Malcolm,

          They do.

          Florida has some of the toughest codes in that regard but I can envision more requirements such as requiring exterior walls to be made of some form of concrete. I don't know about other states along the Gulf Coast and up the Atlantic seaboard (IIRC New Jersey did update their codes after Hurricane Sandy).

          Insurance is driving the changes like it did over a hundred years ago with the creation of building codes Florida is getting closer to crisis mode in terms of premium hikes and insurers leaving the market.

          1. Expert Member
            Malcolm Taylor | | #15

            John,

            That's good to know. Many places here in Canada still are building on flood plains. Every spring, the areas affected are entirely predicable.

  6. Charlie Sullivan | | #8

    I'll give this one a shot:

    "now that we have rid ourselves of vented attics, should we go ahead and bring that space all the way into conditioned space with vaulted ceilings? "

    The only reason I can see to avoid a vented attic is if you plan to put your HVAC equipment in the attic. If you then go with vaulted ceilings, you have lost the advantage that the conditioned attic was supposed to offer. There are lots of other ways to do HVAC, so you might not actually need a conditioned attic. In that case, I'd be inclined to simply go back to a vented attic, unless you want the vaulted ceiling for aesthetic reasons. Even then, I think I'd do a scissors truss and still use blown-in cellulose.

    1. Hugh Stearns | | #11

      Charlie,

      I suspect that I may be missing something here. You seem to be saying that the only reason you would want an unvented attic would be if you are going to put HVAC equipment in the attic. Of course, if you have a gas furnace, you would want to be very careful about that. Ductwork would seem to be the bigger issue, but not the only issue. Placing the thermal line at the roof would seem to be beneficial under any circumstance. As in my area, most ductwork is run in the attic, it would seem better to remove the ceiling and use exposed ducts, which is a significant change to normal residential design. Why does removing the attic change the value of having ducts run through conditioned space? Am I missing something?

      1. Charlie Sullivan | | #17

        When I say "HVAC equipment" I mean all of the above: air conditioning equipment, ductwork, furnaces, ERV, dehumidifiers, etc.

        When you say "Placing the thermal line at the roof would seem to be beneficial under any circumstance," you are probably assuming ducts are in the attic. That's not "any circumstance." There are lots of alternatives to running ducts in the attic. Some of them are:

        * Ductless minisplits.

        * Ducted minisplicts with ducts run in the tops of closets and the like.

        * Ducts in the basement or crawlspace and up through walls and chases.

        * Hydronics systems including mini slim fan coils for room-by-room cooling.

  7. DCContrarian | | #13

    I'll take this one: "It seems wise to bring thermal mass inside the home to moderate heat loads. "

    First off, this is only true on days when the temperature outside goes above and below room temperature. If it's hot all day or cold all day more heat capacity doesn't really help you.

    That said, my experience is that most people who use the term "thermal mass" don't really understand heat capacity. How much something weighs is only one factor in how much heat it holds, the specific heat of the item is also important. Materials like concrete and masonry are dense, but they have low specific heats and hold little heat. Most materials on the interior of a house, like drywall and framing lumber, actually have higher specific heats than concrete. Houses weigh a lot -- like 100,000 lbs -- and a lot of that weight is inside the building envelope. So there is just no practical benefit to trying to make the house any heavier.

  8. Walter Ahlgrim | | #16

    I fail to see any form following any function.

    I see dollars wasted for fashion.

    The only reason to put the HVAC attic is to free up the floor space a unity room full of equipment would require giving the builder who puts the HVAC in the attic a completive advantage and doubling the operating cost to the home owner.

    The only reason to make the surface area of the home 50% bigger by conditioning the attic is half hearted attempt to lower the operating cost from the first poor choice that they are unwilling to reconsider. Then they lay on the really thick spray foam and get what R 25 or 30 that is a joke.
    Conditioning the attic will trim the waste from 50% to 40% making the slightly better than dumb idea of an attic full of HVAC and venting. An attic filled HVAC is a self inflicted wound.

    The only reason the roofs have a steep pitch is that shingling the giant steep roofs cost less than siding walls making building a half stories cost less per square foot.

    Mass wall was the only workable option before AC, today they are non functional fashion statement.

    If you are building spec houses build the fashion statements the market wants at the lowest possible first cost.

    The buyers do not care about the operating cost because they will sell in 6 years or so no time to recover any costs a above code minimum build.

    Walta

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